The complete guide to electrical insulation testing. Let i total initial current during polarization index test or pi test. Polarization index pi, dielectric absorption ratio dar. Test voltages of 500v, v, 2500v, and 5000v measure insulation resistance to 60gohm large 6000 count display with bargraph and backlight polarization index. Polarization index test pi value test along with insulation resistance test ir value test is conducted on hv electrical machine to determine service condition of the insulation. Novel polarization index evaluation formula and fractionalorder. Pdf measurement variations of insulation resistance.
Megger guide to electrical insulation testing pdf instrumart. Therefore, pi megger value after 10 minutes megger value after 1 minute. Along with the insulation testing, insulation resistance ir and polarization index pi techniques are suitable for different types of hv electrical machines and. The purpose of this recommended practice is to a define insulation resistance and polarization index testing of the winding of a rotating machine. Applied technical services offers polarization index testing for clients looking to evaluate the fitness of motors by identifying potential issues such as insulation deterioration and moisture. Find polarization index test related suppliers, manufacturers, products and specifications on globalspec a trusted source of polarization index test information. This test is usually performed in conjunction with the megger test. The principle on which the polarization index test works is based on the idea that impurities in a winding act as charge carriers and cause current leakage. Polarization index test pi the pi test measures the. A test voltage is applied for a fixed period of time, usually 60 seconds and a reading is taken. It is measured as ratio of insulation resistance irfor 10 minutes to insulation. This article will discuss each of the changes referencing directly to. Dielectric absorption test the dielectric absorption or timeresistance test is an extension of the insulation resistance test where instead of a spot test, the testing device is. Polarization index testing benefits polarization index pi testing is an extension of the insulation resistance test and is designed to check specific issues in a motor such as moisture and insulation deterioration.
Power generator and motor ir and pi test importance. The spot reading test should only be carried out when the winding temperature is above the dew point 1. I then use the political polarization index to quantify the e ects of an innovation in the ppi on the real economy. The index provides indication of the amount of impurities in the winding and the cleanliness of it. Polarization index testing applied technical services.
The measurement method using the polarization index is ideal for testing solid insulating circuits. This article will discuss each of the changes referencing directly to ieee std 432000. A value of less than 1 calls for further investigation. Condition assessment of medium voltage underground pilc cables using partial discharge mapping and polarization index test results july 2008 electrical insulation, 1988. Polarization antenna, the state of polarization in the above sense of electromagnetic waves transmitted by or received by a radio antenna. The polarization index pi provides an indication for the level of dirt or moisture buildup. Troubleshooting with insulation resistance test instruments. Plant engineering polarization index testing benefits. Measurement variations of insulation resistancepolarization index during utilizing time in hv electrical machines a survey article pdf available in measurement 59. A dielectric absorption test is a test that checks the absorption characteristics of wet or contaminated insulation. As indicated previously, this direct measurement of the insulation resistance is significantly affected by. Wide range measurement up to 5kv with insulation resistance to 60gohm features.
This gives the absorption polarization current ample time to decay. Polarization index pi for this method, two readings are taken at 1 minute and 10 minutes, respectively. Performed as a step test cables discharged 4 times test duration after test ieee 400 2012 omnibus ieee guide for field testing and evaluation of the insulation of shielded power cable systems rated 5 kv and above. Prior to 1974, the industry relied on nonstandardized systems to evaluate the polarization of the insulation system. In insulation resistance test, a high dc voltage is. The pi test is useful because the remaining variable absorption current indicates the health of the insulation. Polarization waves, the ability of waves to oscillate in more than one direction, in particular polarization of light, responsible for example for the glarereducing effect of polarized sunglasses. Insulation resistance testing guide chauvin arnoux. The ratio without dimensions of the 10minute insulation resistance over the 1minute value is called the polarization index pi and can be used to assess the quality of the. Use polarization index test to determine conditionhealth. Polarization index is the ratio of megger value taken for 10 minutes to the megger value taken for 1 minute. In hv machines and winding are likely to be affected by moisture and contamination.
Understanding insulation resistance testing aemc instruments. This led the ieee to form a standards committee to address this situation. There are five basic causes for insulation degradation. Understanding insulation resistance testing pdf 0712. Measuring resistance can tell you how good the insulation is. For this test, the megohmmeter is connected across the insulation of the windings of the machine being tested. Where the ir test is performed for a period of one minute, the pi test is performed over a period of ten minutes. Perform insulation powerfactor or dissipationfactor tests on all windings in accordance with the test equipment manufacturers published data. The insulation resistance test consists in measuring the insulation resistance of a device under test. The insulation resistance and polarization index tests of an electric motor or generator has been regarded as a useful tool in evaluating its windings for build up of dirt or moisture, deterioration of the insulation, fitness for high potential tests and. Introduction the standard that all of us have lived by for insulation resistance testing was reissued in. Whether you test monthly, twice a year, or once a year depends upon the type, location, and importance of the equipment.
Polarization index test is for the measurement of insulation resistance of rotating machinery rated 1 hp 1 kw or greater. There are 2 test can be performed on a transformer by a megger. The polarization index pi is used as an indicator of motor insulation health, and is useful in identifying accumulation of contaminants as well as physical change in the insulation. This gives the absorption polarization current ample time to decay, and reveals a more detailed indication of the. Ip test is conducted especially to determine the dryness and cleanliness of the insulation. What is polarization index and dielectric absorption ratio.
Capacitance normally only affects the first few seconds of the polarization index pi test. Dar measurement is a diagnostic test similar to the polarization index pi, but dar takes the ratio of the insulation resistance usually measured at 30 sec and 1 min other time settings are possible instead of 1 min and 10 min typically of the pi. Optional perform a powerfactor or dissipationfactor tipup test on windings rated greater than 2. Searching for polarization index pi, dielectric absorption ratio dar and 1 to 15 min. Absorption curve of test conducted on 350 hp motor. Aguide to diagnostic insulation testing above 1 kv 3 ability to maintain a high resistance. Polarization index pi for oilfilled transformers prc electrical 7 sep 06 01. In particular, i analyze changes in employment, output, and investment that. Pdf measurement variations of insulation resistancepolarization.
This test is primarily conducted on form wound motors and generators. C i r e d 19th international conference on electricity distribution vienna, 2124 may 2007 paper04 cired2007 session 1 paper no 04 page 1 4 condition assessment of in sevice medium voltage underground pilc cables using partial. Because of this, it is not recommended for use on equipment. Pdf condition assessment of medium voltage underground. The simplest implementation of the time resistance test for solid insulation is represented by the popular. Dar measurements are useful for instance when the pi is 2 or less even for new objects under test. From a standpoint of physics, to polarize is to cause something to obtain polarity. Polarization index, or pi, is a ratio of the megohms after 10 minutes divided by the megohms after 1 minute. They interact with each other and cause a gradual spiral ofdecline in insulation quality. The polarization index is an indication of the condition of the insulation. The purpose of insulation resistance ir reading is to evaluate the condition of the insulation between conductors and ground.
Timer function for ir measurements, voltage measurement from ohms 0 to 600v with maxmin, peak and relative functions megohmmeters. One simple test that is employed is the polarization index p. Curve d indicates a good insulation with an excellent polarization index of 5. Insulation resistance test and polarization index test. Both insulation resistance test ir value test and polarization index test pi value test are conducted on hv machine to determine service condition of the insulation. Polarization index test pi value test along with insulation resistance test ir value test is conducted on hv electrical machine to. Polarization index pi, insulation to ground tests and ac vs dc testing of insulation systems. Polarization index test free download as powerpoint presentation. For example, a small pump motor or a short control cable may be vital to a process in your plant.
419 370 1580 1326 314 94 829 1060 764 813 1007 1044 707 458 686 1691 77 813 436 1593 414 1188 268 1402 1206 1455 1207 996 261 553 630 659 399 967 153 94 6 991 1494 1254 604 1080 1077 770